The present invention is related to techniques of determining chromatic dispersion in DWDM networks.
DWDM (Dense WDM) networks are optical networks in which optical signals at different wavelengths share an optical fiber. Each wavelength defines a particular communication channel. In a stricter sense, DWDM also refers to an ITU (International Telecommunications Union) standard which includes the specification of the particular channel wavelengths and the spacings between these channels and is based upon WDM (Wavelength Division Multiplexing), an earlier ITU standard in which the channel spacings were further apart and a smaller number of wavelength channels were carried by an optical fiber. It should be noted that the term DWDM, as used herein, refers to the first, more inclusive sense so as to include the ITU WDM and DWDM standards, unless specifically stated otherwise.
The speed of light in an optical fiber varies with wavelength. The resulting chromatic dispersion causes a signal pulse to spread out and become less distinct as it travels along an optical fiber. In optical networks, especially those with high bit rates, compensation for chromatic dispersion must be made for proper network operation. Typically one or more dispersion compensation units (DCUs) are inserted in a network span or link to offset the chromatic dispersion created in the optical signals traveling across the span or link. Thus it is very desirable to obtain an accurate measurement of chromatic dispersion in a span or link to ensure the proper compensation by the DCUs for signals traveling over the span or link. Furthermore, in many cases chromatic dispersion should be determined along the entire network link so that optical signals to and from users at sites along the link are properly compensated.
The present invention provides for a fairly inexpensive way of determining the chromatic dispersion of the optical fiber of a WDM link at one or more sites along the link.